Ultrasonic transmitter/receiver, process for producing the same, and ultrasonic flowmeter

Abstract

An ultrasonic transducer according to the present invention includes a piezoelectric body 2 for transmitting and receiving an ultrasonic wave and acoustic matching layers 3 a and 3 b made of a dry gel. The acoustic matching layers 3 a and 3 b are multiple dry gel layers with mutually different acoustic impedances.

1 . An ultrasonic transducer comprising a piezoelectric body and an acoustic matching member, which is coupled acoustically to the piezoelectric body, 
 wherein the acoustic matching member includes at least two acoustic matching layers, which have mutually different acoustic impedances and each of which is made of a dry gel.    
   
   
       2 . The ultrasonic transducer of  claim 1 , wherein the at least two acoustic matching layers are chemically bonded together at their interface.  
   
   
       3 . The ultrasonic transducer of  claim 1 , wherein each of the acoustic matching layers has a thickness of 2 μm or more.  
   
   
       4 . The ultrasonic transducer of  claim 1 , wherein each said acoustic matching layer made of the dry gel includes a porous structure portion with an average pore diameter of 1 μm or less.  
   
   
       5 . The ultrasonic transducer of  claim 1 , wherein the acoustic impedances of the acoustic matching layers sequentially decrease from the piezoelectric body toward a propagation medium.  
   
   
       6 . The ultrasonic transducer of  claim 1 , wherein the acoustic impedances of the respective acoustic matching layers included in the acoustic matching member all fall within the range of 2.5×10 3  kg/m 2 /s to 1.2×10 7  kg/m 2 /s.  
   
   
       7 . The ultrasonic transducer of  claim 1 , wherein the number of the acoustic matching layers included in the acoustic matching member is two.  
   
   
       8 . The ultrasonic transducer of  claim 1 , wherein the thicknesses of the respective acoustic matching layers included in the acoustic matching member are one-eighth to one-third as long as the wavelength of an ultrasonic wave to be transmitted and received.  
   
   
       9 . The ultrasonic transducer of  claim 1 , wherein the acoustic matching layers included in the acoustic matching member are made of an inorganic material.  
   
   
       10 . The ultrasonic transducer of  claim 9 , wherein the inorganic material is an inorganic oxide.  
   
   
       11 . The ultrasonic transducer of  claim 10 , wherein the inorganic oxide has a hydrophobized solid skeleton.  
   
   
       12 . The ultrasonic transducer of  claim 1 , further comprising a structure supporting member that covers the piezoelectric body, 
 wherein the acoustic matching member is supported on the structure supporting member.    
   
   
       13 . An ultrasonic flowmeter comprising: 
 a flow rate measuring portion, through which a fluid under measurement flows;    a pair of ultrasonic transducers, which is provided for the flow rate measuring portion and which transmits and receives an ultrasonic signal;    a time-measuring portion for measuring time that it takes to propagate an ultrasonic wave between the pair of ultrasonic transducers; and    flow rate calculating means for calculating the flow rate of the fluid based on a signal supplied from the time-measuring portion,    wherein each of the ultrasonic transducers is the ultrasonic transducer of  claim 1 .    
   
   
       14 . The ultrasonic flowmeter of  claim 13 , wherein the piezoelectric bodies of the ultrasonic transducers are shielded from the fluid under measurement.  
   
   
       15 . The ultrasonic flowmeter of  claim 13 , wherein the fluid under measurement is a gas.  
   
   
       16 . An apparatus comprising the ultrasonic transducer of  claim 1 .  
   
   
       17 . A method for fabricating an ultrasonic transducer, the method comprising the steps of: 
 (a) preparing a piezoelectric body, which has a first surface and a second surface that is opposite to the first surface and which includes electrodes on the first and second surfaces, respectively; and    (b) providing two acoustic matching layers of a dry gel, which have mutually different acoustic impedances, on at least one of the first and second surfaces of the piezoelectric body.    
   
   
       18 . The method of  claim 17 , wherein the step (b) includes the steps of: 
 (b1) supplying a first gel material onto at least one of the first and second surfaces of the piezoelectric body;    (b2) forming a first wet gel layer by gelling a solution of the first gel material;    (b3) supplying a second gel material onto the first wet gel layer;    (b4) forming a second wet gel layer by gelling a solution of the second gel material; and    (b5) turning the first and second wet gel layers into a first acoustic matching layer and a second acoustic matching layer, respectively, by drying the first and second wet gel layers.    
   
   
       19 . The method of  claim 18 , wherein the step (b4) includes reforming the first wet gel layer such that the first acoustic matching layer will have its acoustic impedance changed.  
   
   
       20 . The method of  claim 19 , wherein the step (b) further includes the steps of: 
 (b6) supplying a third gel material onto the second wet gel layer; and    (b7) forming a third wet gel layer by gelling a solution of the third gel material,    wherein the step (b5) includes forming a third acoustic matching layer by drying the third wet gel layer.    
   
   
       21 . The method of  claim 17 , further comprising the step of hydrophobizing the wet gel layer(s) before the step (b5).